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Re: [PATCH] V7, #4 of 7, Add explicit (0),1 to @pcrel references
On Mon, Nov 25, 2019 at 05:52:29PM -0500, Michael Meissner wrote:
> On Fri, Nov 22, 2019 at 06:52:42PM -0600, Segher Boessenkool wrote:
> > On Thu, Nov 14, 2019 at 05:51:14PM -0500, Michael Meissner wrote:
> > > In some of my previous work, I had make a mistake forgetting that the PADDI
> > > instruction did not allow adding a PC-relative reference to a register (you can
> > > either load up a PC-relative address without adding a register, or you can add
> > > a register to a constant). The assembler allowed the instruction, but it
> > > didn't do what I expected.
> >
> > So, what was the instruction?
>
> If you write:
>
> paddi 10,9,foo@pcrel
>
> The assembler will interpret this as:
>
> paddi 10,9,(.-foo),0
>
> I.e. it will add the difference from current instruction to foo and register 2
> and place it in register 10. But it will not add the current location for the
> paddi.
>
> Of course it might make sense if the assembler could flag the first line as an
> error, and if you really wanted to write that, you should use:
>
> paddi 10,9,foo@pcrel,0
Does it ever make sense to allow @pcrel on anything that is not prefixed
and R=1? (Cc: Alan).
> > Can you fix this in the caller?
>
> Since the code was invalid, the add insn modification to allow adding an
> address has been removed. It was a suggestion after I made the mistake to make
> sure that nobody else would make that mistake.
>
> As I said, this is an optional patch. The idea was to be helpful to other
> people in the future, in that if they try to generate an add between a register
> and a PC-relative label, that the assembler would give a warnging (due to (0),1
> present).
>
> If you don't think it is important to do that protection, I can leave it out.
That isn't what I said. I'm not happy with how you implemented this,
that's all.
Segher